Properties of Physical Systems: Transient Singularities on Borders and Surface Transitive Zones

Certain alternative properties of physical systems are describable by supports of arguments of response functions (e.g. light cone, borders of media) and expressed by projectors; corresponding equations of restraints lead to dispersion relations, theorems of counting, etc. As supports are measurable, their absolutely strict borders contradict the spirit of quantum theory and their quantum evolution leading to appearance of subtractions or certain needed flattening would be considered. “Flattening” of projectors introduce transitive zones that can be examined as a specification of adiabatic hypothesis or the Bogoliubov regulatory function in QED. For demonstration of their possibilities the phenomena of refraction and reflection of electromagnetic wave are considered; they show, in particular, the inevitable appearing of double electromagnetic layers on all surfaces that formerly were repeatedly postulated, etc. Quantum dynamics of projectors proves the neediness of subtractions that usually are artificially adding and express transient singularities and zones in squeezed forms.     

Junction layer analysis in one-dimensional steady-state Euler-Poisson equations

We study the quasi-neutral limit in one-dimensional steady-state Euler-Poisson equations with junction layers. Typically, the junction layer phenomenon occurs in a ballistic diode of a semiconductor device where the doping profile is a discontinuous function. We derive the junction layer equations and prove the existence of their solutions which decay exponentially. Finally, we justify the quasi-neutral limit with junction layers by giving uniform error estimates.     

Investigations of dynamic photorefractivity regime by optical polarizing microscopy

We present a technique, based on optical polarizing microscopy, and results of direct observation of the optical interference field effect on the transient domains excited by ac electric field in a nematic planar cell with photosensitive aligning layers. The light source used in a microscope operated in DC mode as well as in triggered pulse one. Obtained microscopic snapshots of transient domain structure confirmed our assumption of the transient domains reordering (trapping) by the low intensity optical interference field.     

Rotational diffusion of tungstic acid colloids in microgravity studied by free-fall experiments. Effects of sodium chloride and ethyl alcohol

Rotational relaxation times (τ) of anisotropic tungstic acid colloids in aqueous suspension containing sodium chloride or ethyl alcohol are studied in microgravity achieved by free-fall experiments. Experimental errors at 0 G, in many cases, are small compared with those at 1 G, which is ascribed to the lack of the convection of suspension in microgravity. Much more reliable data of the diffusion coefficients are obtained in microgravity. The limiting slopes of the relaxation curves in the plots of the transmitted-light intensity against time at 1 G depend on the flow direction of the suspension in the flow cell, whereas those at 0 G are close to zero irrespective of the flow direction. Sodium chloride decreases τ, whereas ethanol addition increases this time. These effects are ascribed to the thinning of the electrical double layers and to the increase in the suspension viscosity. Received: 5 July 2000 Accepted: 21 September 2000     

Voltammetry of Metallic Powder Suspensions on Mercury Electrodes

Ultrafine powder samples of Cu, Fe, Ni, Mo and W were examined voltammetrically in aqueous suspensions with hanging mercury drop electrode. According to chemical interaction of the metallic powder particles with the dispersing medium the voltammetric curves either consist of a set of individual current peaks given by particulate reduction of surface oxides on impingements of particles from their suspension upon the electrode, or correspond to electroactivity of dissolved products of chemical reaction between particles and the medium.     

Exponential decay for the solutions of nonlinear elliptic systems posed in unbounded cylinders

We study the asymptotic behavior at infinity of the solutions of a nonlinear elliptic system posed in a cylinder of infinite length. The problem is written in a variational formulation, where we ask the derivative of the solutions to be in Lp. We show that an exponential decay at infinity for the second member implies exponential decay for the derivative of the solutions. We also give an application of this result to the study of boundary layers problems.     

Antibacterial effect of silver modified TiO<Subscript>2</Subscript>/PECVD films

This paper deals with photocatalytic activity of silver treated TiO₂ films. The TiO₂ films were deposited on glass substrates by plasma enhanced chemical vapor deposition (PECVD) in a vacuum reactor with radio frequency (RF) low temperature plasma discharge in the mixture of oxygen and titanium isopropoxide vapors (TTIP). The depositions were performed under different deposition conditions. Subsequently, the surface of TiO₂ films was modified by deposition of silver nanoparticles. Photocatalytic activity of both silver modified and unmodified TiO₂ films was determined by decomposition of the model organic matter (acid orange 7). Selected TiO₂ samples were used for tests of antibacterial activity. These tests were performed on Gram-negative bacteria Escherichia coli. The results clearly proved that presence of silver clusters resulted in enhancement of the photocatalytic activity, which was up to four times higher than that for pure TiO₂ films.     

Structural features of sublimed layers of meso-mono-4-pyridyltriphenylporphyrinatocobalt(ii) and reversible binding of molecular oxygen

The interaction of oxygen with sublimed layers of meso-monopyridyltriphenylporphyrinatocobalt(ii) (CoMPyTPP) was studied by electronic absorption and IR spectroscopy. The reversible binding of O₂ to the axial 5-position was shown for the freshly sublimed layers: the 6-position can either be free, or occupied by the pyridyl group of the adjacent molecule in the layer. The concentration of the complexes of the first type decreases to zero with time, whereas that of the second type complexes increases. The binding of oxygen on the sublimed layers of CoMPyTPP differs substantially from that on meso-tetraphenylporphyrinatocobalt(ii) and meso-tetra-3(4)-pyridylporphyrinatocobalt(ii), which loose their capability of O₂ binding with time.     

Control of surface forces through hydrated boundary layers

Hydration layers surrounding charges or zwitterionic moieties have long been known to play important roles in areas including antifouling and colloidal stability, and particularly over the past 15 years or so, their role in boundary lubrication has been widely investigated. Hydration repulsion because of hydrated ions or polar groups present on surfaces may dominate their interactions at high electrolyte concentrations, so that Derjaguin–Landau–Verwey–Overbeek theory does not apply. Hydration shells, strongly held by the charges they surround, can sustain large pressures without being squeezed out, while by rapidly relaxing, and they behave like a fluid during shear; this may lead to their acting as lubrication vectors with outstanding friction–reduction properties. This review considers hydration layers around trapped ions, polymer brushes, and amphiphiles (surfactants and phosphatidylcholines), focusing on their lubrication properties. Finally, we suggest some prospects for further development of current hydrated vectors and designing new hydrated vectors for modifying surface interactions.     

Ultrathin‐Carbon‐Layer‐Protected PtCu Nanoparticles Encapsulated in Carbon Capsules: A Structure Engineering of the Anode Electrocatalyst for Direct Formic Acid Fuel Cells

Structure engineering is an effective strategy to enhance the performance of electrocatalysts for the formic acid oxidation reaction. However, it remains a challenge to prepare a highly active electrocatalyst based on a distinct understanding of its structure‐dependent performance. The design and synthesis of ultrathin‐carbon‐layer‐protected PtCu nanoparticles (NPs) encapsulated in a N‐doped carbon capsule (PtCu@NCC) is reported. This system is fabricated by using Zn‐based metal–organic frameworks as the carbon support source and metal‐containing tannic acid as the protecting shell template. It displays 9.8‐ and 9.6‐fold enhancements in mass activity and specific activity compared to commercial Pt/C. Moreover, a constructed direct formic acid fuel cell using PtCu@NCC as the anodic electrocatalyst delivers a maximum power density of 121 mW cm^?2. Significantly, PtCu@NCC exhibits superior structural stability and catalytic durability in both half‐cell and full‐cell tests. A mechanism study reveals that the enhanced activity is partially attributed to facilitated electro‐oxidation kinetics of formic acid in the unique structure of PtCu@NCC, while the excellent durability stems from the “protecting effect” of the in‐situ‐formed ultrathin carbon layer on the surface of the PtCu NPs. This work opens a new avenue for the development of high‐performance electrocatalysts for fuel‐cell applications by offering essential insights into the structure–performance relationship of the materials.